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Full text of "Treatise On Applied Analytical Chemistry(Vol-1)"

GERMAN SILVER                                     269

2.  Determination of the Copper and Lead.—In absence of tin, the
nitric acid solution is at once diluted to about 150 c.c. and electrolysed for
the simultaneous determination of the copper and lead (see Electrolytic
Determination of the Copper and Lead in Ordinary Brasses, p. 224).

If, however, the alloy contains tin and the solution is evaporated to
dryness to separate the metastannic acid, the nitrate is treated \\ith 15 c.c.
of nitric acid (D 1-2), diluted to 150 c.c. and electrolysed.

3.  Determination of the Iron.—The liquid from which the copper
and lead have been separated, together with the wash water from the first
beaker, is evaporated until white fumes of sulphuric acid appear, in order
to transform the nickel and zinc nitrates into sulphates ; the 10% sulphuric
acid (20 c.c.) added to the electrolyte is sufficient for this purpose.    When
cold, the residue is taken up with water acidified with sulphuric acid and
heated on the water-bath, the clear solution being treated with a few drops
of hydrogen peroxide and made alkaline with ammonia.    After a short
rest on the water-bath, the precipitate is filtered off, dried, ignited and
weighed :   Fe,03 X 0-6994 — FC-

4.  Determination of the Nickel.—The filtrate from the ferric hy-
droxide is made up to about 150 c.c. and then mixed with 30 c.c. of con-
centrated ammonia and o-i gram of hydroxylamine sulphate, the electrodes
being arranged but the circuit not closed.    A thermometer is fitted and
the beaker covered with the two halves of a clock-glass having gaps for
the stems of the electrodes and for the thermometer and heated to 90°.
One or two drops of fresh concentrated sodium sulphite solution are then
added and the electrolysis immediately started, the temperature being kept
at about 90° and occasional small quantities of ammonia (i vol. cone,
ammonia to I vol. water) added from a wash-bottle to replace that lost
owing to the heating:  Winkler cathode;  spiral Winkler anode, ND100 =
o-i ampere ;   voltage — 2 ;   temperature = 90°;   duration (o-i gram Ni)
about 2 hours.

When the liquid changes from blue to colourless, a drop of it is with-
drawn and treated with alcoholic dimethylglyoxime solution to ascertain
if the nickel is completely deposited. When this is the case, the flame is
extinguished, the thermometer taken out and washed, the cover removed
and the electrolytic beaker replaced by another filled with distilled water.
After some time the cathode is detached, washed with water, alcohol and
ether, dried at 70° and weighed.1

5.  Determination of the Zinc.—In the liquid from which the nickel
has been removed, mixed with the wash water contained in the beaker
and concentrated to about 150 c.c., the zinc is determined by one of the
methods indicated for the electrolytic determination of zinc in ordinary
brasses (see p. 224).

B. Gravimetrically

1. Determination of the Tin, Lead, Copper and Iron.—See Gravi-
metric Analysis of Ordinary Brasses.

1 Under these conditions the nickel and any cobalt present are deposited simul-
taneously. For their separation, see Analysis of Commercial Nickel.                                                                                                                •                                        ^,1